1. Field of the Invention
The present invention relates generally to an apparatus for transferring oriented fibers utilized in making fiber-reinforced sheet molding compound.
2. Background Art
Sheet molding compound (SMC) is generally defined as a composite molding material made up of thermoset polymer material that may be reinforced with a fiber reinforcement. SMC products are molded to form high strength, lightweight, dimensionally stable and corrosion resistant products. SMC products are generally molded in matched die sets that apply heat and pressure to simultaneously cure, or cross-link, the SMC into a desired shape.
Fiber reinforcements in sheet molding compounds are generally deposited in a random orientation when the SMC compound is formed. SMC compounds may be reinforced by chopped fiber rovings, such as glass fiber, natural fibers, aramid, or carbon fiber. The randomly deposited chopped fiber rovings yield isotropic material properties in the molded component. Oriented chopped fibers provide localized areas of directional fiber reinforcement that yield anisotropic material properties. Currently, anisotropic material properties are obtained in SMC compounds by inserting a woven mat having continuous fibers between layers of a carrier polymeric film that is later stripped off of the SMC prior to molding.
One problem with using a continuous fiber woven mat is that the mat is more expensive than a continuous fiber roving. There is a need to weave the fibers together to form the mat. In addition, the woven mat impedes material flow during the molding process because the fiber is both continuous and mechanically connected by weaving. A previous application Ser. No. 11/627,097 filed Jan. 25, 2007, now U.S. Pat. No. 7,691,223, issued Apr. 6, 2010 filed by Applicants and their assignee proposed providing a directionally oriented discontinuous fiber reinforcement to be used in the manufacture of SMC. The oriented fibers provide the SMC with anisotropic stiffness/strength while utilizing low cost continuous roving fiber reinforcements.
SMC having directionally oriented discontinuous fibers provides increased flow properties during the molding process. According to the process proposed, SMC is manufactured utilizing a continuous roving which is then chopped into discontinuous segments of a desired length. Aligning the chopped fiber reinforcements along a common axis provides improved anisotropic material properties in the finished product.
A problem in implementing the process described in Applicants' above invention is that the chopped fibers are difficult to control after chopping as they are conveyed to the SMC carrier film and resin paste in the SMC manufacturing process. After chopping, the chopped fiber is transferred from the chopping unit and tends to fall randomly on the SMC carrier film and resin paste. Random distribution results in SMC that yields isotropic material properties instead of the desired anisotropic properties.